1. Field of the Invention
The present invention relates to a method of press-molding a thermoplastic resin. Hereafter, a thermoplastic resin is referred to as a "resin".
2. Description of the Prior Art
A well known method of press-molding a resin involves supplying a resin in a molten state between a female mold and a male mold which are in an unclosed state. The resin is then compressed between the molds so as to be formed into a predetermined shape. In such a molding method, a short shot of the resin (that is, insufficient filling of the resin into a mold cavity), results in sink or warpage on a surface of a product. There have been efforts to reduce such defects by increasing or reducing a compression rate in a compression step in accordance with the size of the product, so as to absolutely control the compression rate. One such effort is described, for example, in Japanese Patent Kokai No. 241417/1989, and its counterpart U.S. Pat. No. 5,057,255.
However, even the above-mentioned method in which the compression rate is controlled has proven unsatisfactory in preventing defects in the appearance of a resin molded article; surface defects, such as unevenness of gloss and irregularity of the surface of the molded article tend to remain.